Current Status of the SPring-8 Upgrade Project

For many years, scientists around the world have sought an ultra-low-emittance ring-based light source that offers greater performance than existing third-generation light sources. Pioneering work on the seven-bend lattice for MAX IV [1 MAX IV Conceptual Design Report (2006): https://www.maxlab.lu.se/sites/default/files/MAX-IV-CDR_0.pdf [Google Scholar]] initiated these efforts. Another significant development was the scheme for nonlinearity control based on “phase-matched” sextupole pairs. This configuration, first introduced in a light source design by the ESRF design group [2 A. Franchi, Optimization of Dynamic Aperture for the ESRF Upgrade, Workshop on Accelerator R&D for Ultimate Storage Rings, Huairou, Beijing, Oct. 30-Nov. 1 (2012). [Google Scholar]], efficiently suppresses strong nonlinear resonances induced by sextupoles for chromaticity correction. Since a small dynamic aperture due to the strong nonlinearities mentioned earlier presents a great obstacle when we attempt to lower the beam emittance of a high-energy light source using individual bending magnets with small deflection angles, the ESRF scheme contributes significantly to the emittance reduction that can be practically achieved.